High power packages for one or more semiconductor devices such as transistors and diodes have been proposed. One configuration is to place a planar arrangement of semiconductor devices in die form and lead frames upon one metalized substrate, and then place a second metalized substrate over the planar arrangement of semiconductors and lead frames. Direct bond aluminum (DBA) or direct bond copper (DBC) substrates are commonly used that have ceramic cores with a substrate metallization applied to the core prior to assembly with the semiconductor devices and lead frames. The substrate metallization must be thick enough to carry high current (e.g. >10 A) between the semiconductors and the lead frames, and applying a layer that is thick enough is costly. In addition, DBA and DBC substrates for such arrangements must be stress balanced by similar patterns of substrate metallization on both sides of the core to alleviate substrate warping, even if this stress balancing layer is not used to conduct electricity.
Furthermore, the semiconductor devices, an insulated gate bipolar transistor (IGBT) and a diode for example, should be the same thickness as lead frames to provide coplanar bonding-surfaces for the second substrate. However, lead frames with the same thickness as typical semiconductor devices are flimsy, and therefore difficult to handle. If the thickness of the semiconductor devices is increased to match an easy to handle lead frame, the cost and thermal resistance of the semiconductor device are undesirable increased. As such, power packages are typically assembled using lead free solder to overcome thickness variations. However, thick solder joints provide poor thermal and electrical conductivity.